The present invention relates generally to a technique for inspecting materials and testing material integrity. Particularly, the present invention relates to methods and apparatus for testing material integrity via remote field eddy current techniques.
Detecting presence of defects, such as cracks, in materials can assist maintenance technicians in predicting and mitigating likelihood of malfunction in these materials. By way of example, rails and/or railheads in railroad transportation systems can have horizontal defects, transverse defects, and combinations thereof. Generally, horizontal defects in a rail are parallel to a longitudinal axis of the rail. For example, shelling and horizontal split-heads are types of horizontal defects that are commonly found in rails and railheads. Generally, shelling occurs on a surface of the rail when a cold worked layer separates from a bottom layer and flows over the bottom layer. Transverse defects, however, are generally perpendicular to the longitudinal axis of the rail. Under certain conditions, these transverse defects can propagate under the fatigue of cyclic use. Over time, the horizontal and transverse defects (e.g., cracks) can lead to malfunction of the rail and/or railhead, leading to undesirable maintenance costs and downtimes, for instance.
Traditionally, rails and railheads are inspected using both visual and non-visual (i.e., non-destructive) techniques. By way of example, non-destructive testing techniques include ultrasonic techniques (e.g., with forward-looking ultrasonic transducers, side-looking ultrasonic transducers, etc.), electromagnetic techniques such as induction coiled-conductor techniques and magnetic induction techniques to name but a few.
However, these traditional techniques are not without their problems. For example, during ultrasonic testing techniques, horizontal defects can mask transverse defects and, as such, prevent detection of these underlying transverse defects. That is, the horizontal defects (e.g., shelling) can reflect ultrasonic signals, thereby masking the transverse defects located underneath the horizontal defects (e.g. detail fracture in rails). Furthermore, ultrasonic techniques generally limit a speed at which the testing can be conducted.
Furthermore, coiled-conductor induction techniques, which use low frequency power to induce currents in the testing material, are negatively affected by skin effect, which can limit an effective inspection depth of inspection system. Moreover, coiled-conductor induction techniques are also limited by the speed at which the testing can be conducted.
Thus, there exists a need for improved inspection system for detecting defects in the materials to determine the integrity of the material.